Horizontal deflection control means

ABSTRACT

A saturable reactor for providing picture horizontal scan width and scan linearly control for a television horizontal deflection system is connected in series with standard cathode ray tube magnetic-deflection coils. A core of the saturable reactor is adjusted lengthwise of its encompassing coil to vary the scan width by directly altering the inductance of the coil. Independently therefrom, a permanent magnet is rotatably mounted adjacent to one end of the coil opposite of and spaced from an extended portion of the core, the magnet having a preselected one of its poles selectively rotated closer to and further away from the core to vary the scan linearity by directly altering the premagnetization level of the core. The magnet is effective to either add or to buck respectively the induced polarization of the core during periods of forward or reverse deflection current to give linearity control during both the initial and final portions of a sawtooth sweep current waveform having a zeroreference axis.

a States Patent [451 Dec. 19,1972

[54] HORIZONTAL DEFLECTION CONTROL MEANS [72] Inventor: Chris A. Petri,La Grange, 111.

[73] Assignee: Motorola, Inc., Franklin Park, Ill.

[22] Filed: Aug. 3, 1970 [21] Appl. No.: 60,484

[52] US. Cl. ..3l5/27 SR, 315/27 GD [51] Int. Cl ..H01j 29/76 "[58]Field of Search ..3l5/27 SR, 27'GD [56] References Cited UNITED STATESPATENTS 3,153,174 10/1964 Claypool et al ..3l5/27 GD PrimaryExaminerBenjamin A. Borchelt Assistant Examiner-R. KinbergAtt0rneyVincent Rauner and L. Arnold [5 7] ABSTRACT A saturable reactorfor providing picture horizontal scan width and scan linearly controlfor a television horizontal deflection system is connected in serieswith standard cathode ray tube magnetic-deflection coils. A core of thesaturable reactor is adjusted lengthwise of its encompassing coil tovary the scan width by directly altering the inductance of the coil.Independently therefrom, a permanent magnet is rotatably mountedadjacent to one end of the coil opposite of and spaced from an extendedportion of the core, the magnet having a preselected one of its polesselectively rotated closer to and further away from the core to vary thescan linearity by directly altering the premagnetization level of thecore. The magnet is effective to either add or to buck respectively theinduced polarization of the core during periods of forward or reversedeflection current to give linearity control during both the initial andfinal portions of a sawtooth sweep current waveform having azeroreference axis.

5 Claims, 10 Drawing Figures PATEN'IED DEC 19 I972 SHEET 2 BF 2 FIGGBFBG. 6A

FIGB

FIG]? INVENTOR CHRIS A. PETRl w-WM ATTY.

HORIZONTAL DEIFLECTION CONTROL MEANS BACKGROUND OF THE INVENTION Thisinvention relates to a horizontal deflection system of a televisionreceiver, and more particularly it relates to a novel means forcontrolling horizontal scan width and scan linearity for animage-reproducing cathode ray tube.

According to common practice, saturable reactors useful as deflectioncontrol means are connected in series or in shunt with the deflectioncoils of a television horizontal deflection system to provide anon-linear horizontal sweep rate for the tubes electron beam scanningguns in a technique widely known as S-shaping the normal exponentialramp type waveform of the sawtooth deflection current. Additionally,permanent magnets are often magnetically linked with the ferromagneticcore materials of the reactors to affect the level of premagnetizationof the core.

Although it is perhaps more common to utilize this type of saturablereactor as merely a linearity control device, there are devices of thistype being used as both width and linearity control. In one such knowndevice, the saturable reactor is provided with two separate coremembers, one core member for width control and the other for linearitycontrol, only the linearity control core member being magneticallylinked with the magnet. Another existing device of this type has aslideable coil mounted on an elongated core and the combination coil andcore are movable as a unit closer to or father away from the associatedmagnet. The coil is adjusted along the length of the core to vary thescan linearity by varying the slope of the inductance-instantaneousdeflection current characteristic curve within the range of the usefulcurrent. The scan width is adjusted by moving the coil and core unitwith respect to the magnet, which movement directly varies theinductance of the coil without affecting the slope of theinductance-current characteristic curve.

Furthermore, prior art methods of linearity control most commonlyinvolve adjusting the final exponential slope of the deflection currentwaveform to obtain a slower rate of sweep. This single adjustment to theexponential current wave form however is generally unsatisfactory in ofitself in that the initial rise of the deflection current must also bemade slower. Prior art devices also utilize the imposed magnetic fieldof the associated magnet to shift the hysteresis loop characteristiccurve of the core so as to allow the initial portion of the exponentialcurve waveform to be adjusted and leaving the proper slope of the finalportion of the current waveform to be obtained by a judicious choice ofthe circuit parameters. While this latter type of device is animprovement of the former which failed to adjust the initial portion ofthe sweep current, it is nevertheless desirable to be able to adjustboth the initial and the final portion of the sweep current waveform bymeans of the imposed magnetic field. This, of course, cannot beaccomplished by a mere unindirectional shift of the hysteresis loop ofthe core. Also, it is desirable to provide a width-linearity controlmeans having only one core member to allow for an improved device of lowcost and compact size and construction.

SUMMARY It is therefore an object of this invention to provide animproved device wherein a single core member is adjustable axially withrespect to an encompassing helical coil and is adjustably linked with amagnetic field of a magnet to control respectively the scan width andscan linearity of a television horizontal deflection system.

It is another object of this invention to provide a novel means ofaltering horizontal scan width and scan linearity respectively bydirectly varying the amount of additive series inductance of a helicalcoil and the premagnetization level of the core member.

It is still another object to provide scan linearity control by properlyS-shaping the deflection coil current waveform both during the initialrise and during the final exponential portion thereof.

It is yet another object to provide an improved device having a magnetadjustable to compensate for the polarity with which the helical coil isconnected in series with the deflection coil.

Further, it is an object of the invention to provide a much improvedhorizontal deflection control means having a simple construction of lowcost and compact size.

In a preferred embodiment of the invention, a com bination horizontalwidth and linearity control means is connected in series with thedeflection coils of the standard television horizontal deflectioncontrol system and has a helical inductor coil with a longitudinal axis,a ferromagnetic core member core member having a length greater than thelongitudinal length of the coil with one end portion of the core memberadjustably inserted within the coil and another end portion thereofextending from one end of the coil, said core member being movable alongthe longitudinal axis of the coil to provide a means of adjusting thescan width by directly varying the effective inductance of the coil, anda permanent magnet.

The permanent magnet has a rotational axis parallel to and spaced formthe longitudinal axis of the coil and is mounted adjacent one end of thecoil opposite of and spaced from the extending end portion of the coremember in order to control the premagnetization level thereof. Themagnet is magnetized so as to present poles of opposite polarity at twodiametrically opposite points on its periphery. A selected one of thesepoles is aligned directly opposite said other end portion of the coremember for maximum premagnetization thereof, and is rotated in eitherdirection away therefrom for lessening the premagnetization level. Also,the magnet is effective to either add to or buck respectively theinduced polarization of the core member during forward or reversedeflection current in order to provide scan linearity control duringboth the initial and final portions of the sawtooth sweep currentwaveform. The rotation of the magnet with respect to the core memberfurther provides an adjustment to the linearity control in both theinitial and final portions of the deflection current waveform.

Other objects and advantages of the invention will occur to thoseskilled in the art as the invention is described in connection with theaccompanying drawing, in which:

THE DRAWING FIG. l is a simplified schematic illustration of ahorizontal deflection system for a television receiver useful inexplaining the principles of the present invention;

FIG. 2 is a schematic circuit diagram of the horizontal deflectionsystem of FIG. 1, showing a schematic representation of the linearityand width control means in series connection with the horizontaldeflection coils;

FIG. 3 is an elevational side view of a preferred embodiment of thelinearity and width control means of the present invention;

FIG. 4 is an end view of the device of FIG. 3;

FIG. 5 is a perspective view of the device of FIGS. 3 and 4, having acutaway portion of the coil and coil form for showing the adjustable endportion of the core;

FIG. 6 is an elevational side view of the isolated operable parts of theembodiment of FIG. 3;

FIG 6A is a diagram representation of the bucking magnetic fields of theembodiment of FIG. 6;

FIG. 6B is a diagram representation of the adding magnetic fields of theembodiment of FIG. 6;

FIG. 7 includes graphs of a normal deflection current waveform and twoS-shaped deflection current waveforms illustrating the line scanlinearity control of the present invention; and

FIG. 8 is a view taken along line 8-8 of FIG. 6.

DETAILED DESCRIPTION FIG. 1 shows a horizontal deflection system 10 as apart of a television receiver having a receiving antenna 11 and acathode ray tube (CRT) 12, fed by a video amplifier l3 and a highvoltage (I-IV) power supply 14 as is standard for television receivers.The yoke 12a of the tube 12 has horizontal magnetic-deflection coils,indicated at 15, which coils carry a sawtooth waveform deflection sweepcurrent 17 supplied by the horizontal oscillator 19 and amplified by thehorizontal output amplifier 21 in a well known manner.

FIG. 2 shows a more detailed schematic circuit diagram of the horizontaldeflection system 10 wherein a horizontal driver circuit 19a of theoscillator 19 supplies the sawtooth waveform deflection current 17 to atransistorized deflection amplifier 21a of the horizontal outputamplifier 21. The amplified sweep current 17 is provided a DC return bythe primary winding 25-26 of the high voltage autotransformer 23 that isconnected to the B+ high voltage power supply 14. The secondary winding26-27 of the autotransformer 23 supplies the operating high voltage tothe CRT 12 through the high voltage rectifier 28 and the anode terminal29. The horizontal deflection coils a and 15b are connected in serieswith the horizontal width-linearity control means 30 of the presentinvention and an AC coupling capacitor 24. The control means 30 includesan inductance coil 31, ferromagnetic core member 32, and permanentmagnet 33; the control means 30 is then connected to ground potential.

For wide angle tube screens, the ramp portion of the sawtooth deflectioncurrent common to horizontal deflection systems, is generallyexponential in its waveform: the pattern characterized by a fast risingcurrent initially, then slowly decreasing in its rate of rise as thedeflection coils begin to build a counter electromagnetic force (EMF),and finally rapidly decreasing as the full counter EMF is developed. Thedeflection current is then said to be at its saturation level.

According to common practice, deflection control means comprising anadditional inductance having a high permeability core, such as iron or aferromagnetic material, is inserted in series or shunt with thedeflection coils to vary the coil inductance by a desired amount. Thisadditional inductance, as taken for example in a series connection,imparts to the deflection current waveform a slower initial rate of riseand therefore gives the desirable S-shaped waveform common to horizontaldeflection systems. With the aid of the S- shaping inductor, the linescanning motion of the electron beam is slower at the beginning of itshorizontal sweep, faster during the central portion of the trace, andslower at the end thereof, thus compensating for the tendency of aconstantly moving beam to appear to be moving faster at both edgeportions of a generally wide flat screen surface than that movement ofthe beam in the central portion of the screen.

A preferred embodiment of the control means 30 of the present inventionis shown in FIGS. 3-5. The control means 30 utilizes a single pieceholder member 35 made of a suitable insulating material. The holdermember 35 has a magnet holding section 35a, a core holding section 3517,and a mounting base 350 with appropriate means for mounting the controlmeans 30 to a circuit board as by apertures 35d. An elongated helicalcoil 37 having two electric connecting terminals 37a and 37b is woundabout a coil form 38 and one end portion of the coil form 38 insertedinto a channel 35e in the core holding section 35b of the holder member35. Thereafter, a ferromagnetic core member 39 (alternatively, the corematerial could be made of iron) is inserted intothe coil form 38, whichacts as an extension of the channel 352 through the helical coil 37.

The coil 37 is seen to have a longitudinal axis that is substantiallyconcentric with that of the core member 39. The core member 39preferably has a length greater than the helical coil 37 so that thecore 39 has a substantial portion within the coil 37 and anotherpreferably substantial opposite portion extending from the coil 37. Theportion of the core member 39 that lies within the coil 37 (or,optionally, the opposite portion thereof) can be provided with atool-accommodating aperture 39a for adjusting the core member 39lengthwise with respect to the coil 37 along its longitudinal axis.

A permanent magnet 41, conveniently constructed in the form of anelongated cylinder and magnetized across its diameter to have twodiametrically opposite magnetic poles on its periphery (a north (N) poleand a south (S) pole together with an accompanying magnetic field), isinsertably mounted for retention in the magnet holding section 35a. Themagnet 41 has a rotational axis parallel to and spaced from thelongitudinal axis of the coil 37 and core member 39, which magnet 41 canas well be provided with a tool-accommodating aperture 41a for rotatablyadjusting the magnetic field of the magnet 41 with respect to theopposite end portion of the core member 39.

l060ll 0620 The operation of the control means 30 to adjust horizontalscan width can best be illustrated by the isolated view of FIG. 6wherein the holder member 35 and the coil form 33 have been omitted andthe operable parts have been maintained in their normal orientation. Ifthe core member 39 is adjusted to move along its longitudinal axis or,optionally along the longitudinal axis of the coil 37, in the directionof the arrow 43, the right-end of the core member 39 as viewed in FIG. 6is caused to move through the coil 37. This movement rapidly reduces thelength of the ferromagnetic core member 39 which lies internal to thecoil 37. By reason of the well understood principles of saturablereactors, this results in a direct variation of the reactance orinductance of the coil 37. The change in inductance of the coil isutilized for providing the line scan width control.

It is obvious that while the exact length of the core member 39 is notcritical, the approximate length should be such that a relatively smallamount of movement of the core 39 in the direction of the arrow 43causes the length of the core path within the coil 37 to vary. The exactlength of the opposite extended portion also is not critical; the magnet41 could overlie somewhat the adjacent end of the coil 37 withoutdegrading appreciable the operation of the control means 30. Also, sincethe magnet 41 and the extended portion of the core 39 cooperate toaffect line scan linearity rather independently of the line scanamplitude or width, as will be described more fully hereinafter, themagnet 41 could be removed at any convenient distance from the coil 37along the length of the core 39 as long as the impractical effects ofmaking the extended end portion of the core 39 too long aresimultaneously considered.

The line scan width and line scan linearity controls are independentadjustments as is readily apparent when observing the movement of thecore 39 with respect to the coil 37 during the adjustment of the linescan width. This is for the reasons that the length of the core member39 adjacent the magnet 41 remains substantially a constant and that thecores movement is in a direction substantially perpendicular to thedirection of the lines of force comprising the magnetic field of themagnet 41.

FIG. 7 shows variations of the ramp portion only, indicated at $5, 47and 47, of the sawtooth deflection sweep current 17 centered about azero reference so as to present forward i) and reverse i) currentportions thereof. The dashed line 45 represents an approximation of thewaveform that the ramp portion of the sweep current 17 would takethrough the deflection coils a and 15b if the linearity correction werenot provided. As stated previously, the ramp portion of the deflectioncurrent has an initial fast rise, slower middle trace and still slowerfinal exponential portion settling slowly to maximum forward current.This type of waveform is undesirable and requires correction to a slowerinitial rise. Also, in order to avoid undue difficulty in malting ajudicious choice of circuit parameters the final exponential rise can beregulated by the control means 3th. The waveform would then require aslight correction to increase the slope of the final exponential rise.This correction is then called S-shaping because of the resemblance ofthe corrected ramp current waveform to the letter S.

With the proper S-shaping, line scan linearity control is obtained. Theoperation of the control means 30 to adjust horizontal scan linearity isbest illustrated by FIG. 6A, 6B and 8. The permanent magnet 41 has itsattendant magnetic field linked with the extended end portion of thecore member 39 so long as the spacing between the magnet 41 and the coremember 39 is not unduly large. This results in the common phenomenonknown as premagnetization of the core member 39. Briefly,premagnetization of the core member 39 increases the flux density of thecore tending to saturate the core more quickly with a given current inthe coil 37.

As shown in FIG. 6A, when the instantaneous AC deflection current 17begins its ramp portion in the form of the reverse current i), thereverse current fiows through the series additive coil 37 and induces atemporary magnetic field surrounding the coil 37, which field permeatesthe ferromagnetic core member 39. In accordance with well understoodprinciples of electromagnetic field theory, the current flow though thecoil 37 induces a magnetic field around the coil 37 having a magneticpolarity with north (N) and south (S) poles according to the directionof the windings of the coil 37 about the core member 39 and thedirection of the current flow though the coils. Thus, the proximity of aselected pole of the magnet 41 to the adjacent end portion of the coremember 39 will have an attraction or repulsion effect upon the adjacentportion of the magnetic field of the coil 37 depending upon whether theinduced polarization of the core member 39 is an opposite or like poleto the selected pole of the magnet 41.

It is readily obvious that in the case of the reverse current i) flowingthrough the coil 37, the desired effect would be to create repulsionforce between the two adjacent poles so as to buck the adjacent portionof the induced magnetic field of the core member 39 and thus slow theotherwise fast initial rise of the ramp current. Therefore, thedirection of the coil windings about the core 39 should be such that thereverse current induces a magnetic field having a south (S) polarity ifthe magnet 41 has a south (S) pole aligned oppositely of the core 39, oralternatively, a north (N) polarity if the magnet 41 has a north (N)pole aligned oppositely of the core 39.

If the terminals 37a and 37b of the coil 37 are connected in reverse tothe magnetic-deflection coils 15a and 15b, the correct polarities of therespective fields can be obtained by merely rotating the magnet 41 untilthe opposite pole is aligned with the core 39. For illustrationpurposes, the magnetic field of the magnet 41 as it links with the core39 has been omitted in FIGS. 6A and 6B and only the diagrammaticalrepresentation of the effect of the repulsion forces between the twolike poles (8-8) and the attraction forces between the two unlike poles(N-S) upon the induced magnetic field of the coil 37 is shown.

Obviously, as indicated by the diagrammatical representation in FIG. 6Bof the additive effect of two unlike poles (N-S) upon the inducedmagnetic field of the coil 37, the forward (+1) deflection currentinduces a polarization in the core 39 wherein the opposite pole islocated in the extended end portion thereof, thus the complementarymagnetic fields of the coil-core and magnet-core combinations have theeffect of increasing the slope of the exponential trace of the forwardcurrent.

In summary, it is readily seen that in FIG. 6A, the like adjacent poles(-8) of the core 39 and the magnet 41 repel to buck the induced magneticfield of the coilcore combination and slow the'initial rise of thereverse current, and that in FIG. 6B, the unlike adjacent poles (N-S) ofthe core 39 and the magnet 41 attract to add to or aid the same magneticfield and speed up slightly the final exponential trace of the forwardcurrent. Also, if the polarity of the coil 37 is reversed in its serialconnection with the deflection coils a and 15b, the magnet 411 couldsimply be rotated 180 about its rotational axis to align the oppositepoles adjacent to the core member 3 to obtain the desired bucking andadding effect of the two magnetic fields during reverse and forwardcurrent flow respectively.

Therefore, it is seen that by placing the magnet 41 in the position withrespect to the core member 39 as indicated in the drawings, line scanlinearity control is obtained. In FIG. 7, the current waveforms 47 and47' are indicative of the linearity corrections realized by theS-shaping effect of the additive and diminutive magnetic forces upon theinduced magnetic field of the coil 37. Further, the rotationalcapability of the magnet 41 about its axis, as best illustrated in FIG.8, will result in increasing or decreasing, respectively, thesecorresponding additive or diminutive forces, and thus the level ofpremagnetization of the core member 39.

The current waveform 47 indicates the maximum amount of linearitycorrection and corresponds to the position of the magnet 41 where thefull strength of the magnets appropriate pole is aligned directlyopposite the core member 39. As the magnet is rotated in the directionof the arrows 51 and 51' to thus align points A or B directly oppositethe core member 39, the effect of the magnets magnetic field upon theadjacent pole of the core member 39, and thus the field of the core 37,is gradually lessened and the S-shaped curve 47' is realized.

FIG. 8 shows line A B which represents the neutral or demagnetizedportion of the magnet 41, and as the magnet is further rotated in thedirections of the arrows 51 and 51 to align the points A or 8' directlyopposite the core member 39, the effect of the magnets magnetic fieldupon the adjacent portion of the induced magnetic field of the coil 37is at its minimum level. At this minimum level, the curve 45 issubstantialy realized although in practice the effect of the magnetsmagnetic field is not entirely eliminated due to the narrowness of sucha theoretical neutral point on the magnet 41. Therefore, the improvedconstruction of the applicants control means 3&1 provides an adjustablerange of linearity control by merely a slight rotation of the magnet 41by means of its tool-receiving aperture 41a.

The invention has been described in detail with particular reference tothe drawings, but it will be understood by those skilled in the art towhich the invention pertains that various modifications and variationcan be made without departing from the spirit and scope thereof, and tothis extend the appended claims are intended to cover the same.

Iclaim:

1. A horizontal deflection control means for connection with atelevision magnetic-deflection coil having a bidirectional currenttherethrough of a type in which the control means provides both electronbeam horizontal line scan width and scan linearity adjustmen'ts, saidcontrol means comprising: an elongated helical inductor coil having alongitudinal axis and adapted to be connected with themagnetic-deflection coil, a double-ended ferromagnetic core memberhaving one end portion adjustably inserted within the helical coil andanother end portion extending from one end of the helical coil, saidcore member being movable along the longitudinal axis of the coil toadjust the insertion of said one end portion within the coil fordirectly adjusting the inductance of the coil whereby the horizontalline scan width is controlled, and a permanent magnet rotatably mountedadjacent said core for varying the amount and polarity of magnetic fluxlinkage between said permanent magnet and said core with rotation ofsaid permanent magnet and said magnet being operative upon rotationthereof to adjust the level of premagnetization of said core whereby thehorizontal line scan linearity is controlled.

2. A horizontal deflection control means as claimed in claim 1 wherein:said magnet is an elongated generally cylindrical magnet having alongitudinal axis with said magnet being mounted for rotationthereabout, and said magnet is further mounted so that said longitudinalaxis is in parallel alignment with and spaced from the longitudinal axisof said helical coil.

3. A horizontal deflection control means as claimed in claim 1 whereinsaid helical coil is connected in series with the magnetic-deflectioncoil.

4. A horizontal deflection control means as claimed in claim 1 whereinsaid magnet and said other end portion of the core member are mountedwithin a single piece holder member having a mounting base and a pair ofparallel spaced channel-like openings for respectively receiving saidmagnet and said other end portion of the core member, a first of saidpair of openings has a diameter slightly larger than the diameter ofsaid magnet and has said magnet concentrically disposed therein wherebythe magnet is free to rotate about its axis within said first opening,and a second of said pair of openings has a diameter slightly largerthan the diameter of said core member and has said other end portion ofthe core member concentrically disposed therein whereby said core memberis free for axial movement within said second opening.

5. A horizontal deflection control means as claimed in claim 4 wherein agenerally tubular coil form has one end portion thereof inserted intosaid second opening and another end portion thereof extending outwardlyfrom one end of said second opening whereby said other end portion ofthe coil form comprises an extension of said second opening, said coilis wound about said other end portion of the coil form with one endthereof adjacent said magnet, and said core member is concentricallydisposed within said coil form and is free for axial movement withrespect thereto whereby said core member has its one end portionencompassed by said coil and its other end portion extended inoppositely spaced relationship to said magnet.

1. A horizontal deflection control means for connection with atelevision magnetic-deflection coil having a bidirectional currenttherethrough of a type in which the control means provides both electronbeam horizontal line scan width and scan linearity adjustments, saidcontrol means comprising: an elongated helical inductor coil having alongitudinal axis and adapted to be connected with themagnetic-deflection coil, a double-ended ferromagnetic core memberhaving one end portion adjustably inserted within the helical coil andanother end portion extending from one end of the helical coil, saidcore member being movable along the longitudinal axis of the coil toadjust the insertion of said one end portion within the coil fordirectly adjusting the inductance of the coil whereby the horizontalline scan width is controlled, and a permanent magnet rotatably mountedadjacent said core for varying the amount and polarity of magnetic fluxlinkage between said permanent magnet and said core with rotation ofsaid permanent magnet and said magnet being operative upon rotationthereof to adjust the level of premagnetization of said core whereby thehorizontal line scan linearity is controlled.
 2. A horizontal deflectioncontrol means as claimed in claim 1 wherein: said magnet is an elongatedgenerally cylindrical magnet having a longitudinal axis with said magnetbeing mounted for rotation thereabout, and said magnet is furthermounted so that said longitudinal axis is in parallel alignment with andspaced from the longitudinal axis of said helical coil.
 3. A horizontaldeflection control means as claimed in claim 1 wherein said helical coilis connected in series with the magnetic-deflection coil.
 4. Ahorizontal deflection control means as claimed in claim 1 wherein saidmagnet and said other end portion of the core member are mounted withina single piece holder member having a mounting base and a pair ofparallel spaced channel-like openings for respectively receiving saidmagnet and said other end portion of the core member, a first of saidpair of openings has a diameter slightly larger than the diameter ofsaid magnet and has said magnet concentrically disposed therein wherebythe magnet is free to rotate about its axis within said first opening,and a second of said pair of openings has a diameter slightly largerthan the diameter of said core member and has said other end portion ofthe core member concentrically disposed therein whereby said core memberis free for axial movement within said second opening.
 5. A horizontaldeflection control means as claimed in claim 4 wherein a generallytubular coil form has one end portion thereof inserted into said secondopening and another end portion thereof extending outwardly from one endof said second opening whereby said other end portion of the coil formcomprises an extension of said second opening, said coil is wound aboutsaid other end portion of the coil form with one end thereof adjacentsaid magnet, and said core member is concentrically disposed within saidcoil form and is free for axial movement with respect thereto wherebysaid core member has its one end portion encompassed by said coil andits other end portion extended in oppositely spaced relationship to saidmAgnet.